U.S. patent application number 11/008380 was filed with the patent office on 2005-07-21 for fuel supply system for an internal combustion engine.
Invention is credited to Frenz, Thomas, Herforth, Andreas, Posselt, Andreas, Schelhas, Peter.
Application Number | 20050155582 11/008380 |
Document ID | / |
Family ID | 34716575 |
Filed Date | 2005-07-21 |
United States Patent
Application |
20050155582 |
Kind Code |
A1 |
Schelhas, Peter ; et
al. |
July 21, 2005 |
Fuel supply system for an internal combustion engine
Abstract
A fuel supply system (2) for an internal combustion engine (1)
for, in particular, a motor vehicle. The fuel supply system (2) is
used for delivering fuel from a fuel tank (3) into at least one
intake manifold (4) or at least one combustion chamber (5) of the
internal combustion engine (1) and includes at least two fuel pumps
(6, 8; 11) connected in series. In order to ensure that the
internal combustion engine (1) is supplied with fuel at any
operating point of the internal combustion engine (1), it is
provided that at least two of the fuel pumps (6, 8; 11) of the fuel
supply system (2) take the form of electric fuel pumps (6, 8). The
second electric fuel pump (8) in the direction of flow is
preferably adjusted to a separate, variable pressure level in a
demand-responsive manner, so that the pressure and fuel quantity
are controlled.
Inventors: |
Schelhas, Peter; (Stuttgart,
DE) ; Frenz, Thomas; (Noerdlingen, DE) ;
Posselt, Andreas; (Muehlacker, DE) ; Herforth,
Andreas; (Leonberg, DE) |
Correspondence
Address: |
KENYON & KENYON
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
34716575 |
Appl. No.: |
11/008380 |
Filed: |
December 8, 2004 |
Current U.S.
Class: |
123/497 |
Current CPC
Class: |
F02M 69/46 20130101;
F02M 37/18 20130101; F02D 33/006 20130101; F02M 37/0047 20130101;
F02M 59/16 20130101; F02M 69/02 20130101; F02M 37/10 20130101; F02M
37/0088 20130101 |
Class at
Publication: |
123/497 |
International
Class: |
F02M 037/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 15, 2004 |
DE |
10 2004 002 139.2 |
Claims
What is claimed is:
1. A fuel supply system for an internal combustion engine (1) for
delivering fuel from a fuel tank (3) into at least one intake
manifold (4) or at least one combustion chamber of the internal
combustion engine (1), comprising at least two fuel pumps (6, 8;
11) connected in series, wherein at least two of the fuel pumps (6,
8; 11) of the fuel supply system (2) take the form of electric fuel
pumps (6, 8).
2. The fuel supply system (2) as recited in claim 1, wherein the
fuel supply system (2) has at least one mechanically driven,
high-pressure pump (11) situated hydraulically nearer to the
internal combustion engine (1) than the electric fuel pumps (6,
8).
3. The fuel supply system (2) as recited in claim 1, wherein the
fuel pumps (6, 8) of the fuel supply system (2) are exclusively
electric fuel pumps (6, 8).
4. The fuel supply system (2) as recited in claim 2, wherein the
fuel supply system (2) has exactly two electric fuel pumps (6, 8)
connected in series.
5. The fuel supply system (2) as recited in claim 1, wherein the
fuel supply system (2) has control means for adjusting the fuel
delivered by the electric fuel pump (8) situated hydraulically
nearest to the internal combustion engine (1), to a specifiable
pressure level.
6. The fuel supply system (2) as recited in claim 5, wherein the
control means adjust the fuel delivered by the electric fuel pump
(8) situated hydraulically nearest to the internal combustion
engine (1), to the specifiable pressure level in a
demand-responsive manner.
7. The fuel supply system (2) as recited in claim 5, wherein the
specifiable pressure level is variable.
8. The fuel supply system (2) as recited in claim 5, wherein the
control means have a control unit (29) for switching on and off the
electric fuel pump (8) situated hydraulically nearest to the
internal combustion engine (1) or for varying speed of this
electric fuel pump (8).
9. The fuel supply system (2) as recited in claim 5, wherein the
control means have a controllable control element (42), which is
situated in a return line (41) from a pressure side of the electric
fuel pump (8) situated hydraulically nearest to the internal
combustion engine (1), to the fuel tank (3), or to the suction side
of this electric fuel pump (8).
10. The fuel supply system (2) as recited in claim 9, wherein the
control element (42) is electrically controllable, and the control
means have a control unit (29) for controlling the control element
(42).
11. The fuel supply system (2) as recited in claim 10, wherein the
control element (42) takes the form of a pulse valve.
12. The fuel supply system (2) as recited in claim 10, wherein the
control element (42) takes the form of a proportional fuel-quantity
control valve.
13. The fuel supply system (2) as recited in claim 9, wherein the
control element (42) takes the form of a mechanical pressure
regulator (43) for adjusting the pressure prevailing on the
pressure side of the electric fuel pump (8) situated hydraulically
nearest to the internal combustion engine, to the specifiable
pressure level.
14. The fuel supply system (2) as recited in claim 13, wherein each
of the electric fuel pumps (6, 8) of the fuel supply system (2) is
assigned a mechanical pressure regulator (43, 44), the pressure
regulators (43, 44) each being situated in a return line (41) from
a pressure side of one of the electric fuel pumps (6, 8) to the
fuel tank (3), or to the suction side of this electric fuel pump
(6, 8), and the pressure regulators (43, 44) adjusting the
pressures prevailing on the pressure sides of the electric fuel
pumps (6, 8) to different pressure levels.
15. The fuel supply system (2) as recited in claim 14, wherein the
pressure levels increase from the first electric fuel pump (6) to
the electric fuel pump (8) positioned nearest to the internal
combustion engine.
16. The fuel supply system (2) as recited in claim 13, wherein all
of the electric fuel pumps (6, 8), filters (7), control element
(42), and pressure regulators (43, 44) are situated in the fuel
tank (3) or in a module to be built into the fuel tank (3).
17. An internal combustion engine (1) for a motor vehicle, having a
fuel supply system (2) for delivering fuel from a fuel tank (3)
into at least one intake manifold (4) or at least one combustion
chamber (5) of the internal combustion engine (1), the fuel supply
system (2) including at least two fuel pumps (6, 8; 11) connected
in series, wherein the fuel supply system (2) is formed as recited
in claim 1.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a fuel supply system for an
internal combustion engine of, in particular, a motor vehicle. The
fuel supply system is used for delivering fuel from a fuel tank
into at least one intake manifold or at least one combustion
chamber of the internal combustion engine. The fuel supply system
includes at least two fuel pumps connected in series.
[0002] The invention also relates to an internal combustion engine
for, in particular, a motor vehicle. The internal combustion engine
includes a fuel supply system for delivering fuel from a fuel tank
into at least one intake manifold or at least one combustion
chamber of the internal combustion engine. The fuel supply system
includes at least two fuel pumps connected in series.
DESCRIPTION OF RELATED ART
[0003] Fuel supply systems of the type mentioned at the outset are
known from the related art. Using such a fuel supply system, fuel
can either be injected into an intake manifold of an internal
combustion engine (so-called manifold injection) or directly
injected into the combustion chambers of the internal combustion
engine (so-called direct injection). Using the fuel pumps situated
in the fuel supply system, fuel is drawn out of a tank and
transported in the direction of the internal combustion engine.
[0004] A fuel supply system for a manifold injection system
normally has a fuel pump taking the form of an electric fuel pump.
The electric fuel pump may be combined with a fuel filter to form a
module to be built into the fuel tank. The electric fuel pump
normally has an electronic demand-control unit in the low-pressure
circuit, i.e. on the suction side. Pressures of, for example, 3 to
6 bar can be generated with the aid of the electric fuel pump.
[0005] Fuel supply systems are known for direct-injection gasoline
engines, those fuel supply systems having, in addition to the
electric fuel pump functioning as a presupply pump, at least one
further fuel pump which is connected in series with the electric
fuel pump and takes the form of a high-pressure fuel pump. The
high-pressure fuel pump is preferably mechanically driven by the
internal combustion engine, via a camshaft or the like. In the case
of direct-injection gasoline engines, the high-pressure fuel pump
can increase the relatively low pressures generated by the electric
fuel pump to, e.g. 120 to 150 bar, and, in the case of
direct-injection diesel engines, to approximately 1,300 to 1,500
bar.
[0006] In the known fuel supply systems for a manifold injection
system, the electric fuel pump is used as the sole fuel pump by
which the injection pressure is generated. However, in fuel supply
systems for direct injection, the electric fuel pump is only used
as a presupply pump. The actual injection pressure is generated by
the high-pressure pump situated downstream in the direction of
flow.
[0007] In operating phases of the internal combustion engine,
during which there is an increased demand for fuel, in particular
when operating the internal combustion engine in the part-throttle
and full-throttle ranges, known fuel supply systems have the
problem that it is impossible to adjust, or to adequately adjust,
the quantity [flow rate] and pressure of the electric fuel pump.
Thus, it cannot always be ensured that the internal combustion
engine is reliably powered in these operating phases.
SUMMARY OF THE INVENTION
[0008] Therefore, the object of the present invention is to supply
fuel to an internal combustion engine in an improved manner, in
particular in operating phases of the internal combustion engine in
which the fuel-quantity demand is increased.
[0009] To achieve this object, the invention provides that,
starting out from the fuel supply system of the species mentioned
at the outset, at least two of the fuel pumps of the fuel supply
system take the form of electric fuel pumps.
[0010] Thus, the present invention provides for the one electric
fuel pump normally used in fuel supply systems of the related art
to be replaced by at least two electric fuel pumps, which are
connected in series and take the form of separate pump stages. This
allows the pressure and quantities [flow rates] of the second and
any subsequent electric fuel pumps in the direction of flow to be
adjusted to a separate, variable pressure level, in a
demand-responsive manner. An important advantage of the fuel supply
system is also that, with the aid of the second and all
post-connected electric fuel pumps, the attainable pressure level
may be increased and flexibly adjusted to any values within a
specifiable pressure range. In addition, continuous fuel-quantity
[flow-rate] and pressure adjustment may be carried out when
operating the internal combustion engine in the part-throttle and
full-throttle ranges.
[0011] The fuel supply system of the present invention provides
that, in addition to a conventional electric fuel pump, at least
one further electric fuel pump be positioned downstream from it in
a fuel path from a fuel tank to the internal combustion engine.
This additional electric fuel pump allows the fuel pressure of,
e.g. approximately 2.5 to 5 bar on the pressure side of the first
electric fuel pump to be increased to approximately 8 to 15 bar on
the pressure side of the second electric fuel pump. The second and
each post-connected electric fuel pump may be activated during
specific engine operating phases, in which the fuel-quantity demand
is increased. For example, in addition to the first electric fuel
pump, the further electric fuel pumps may be activated during a
starting phase of the internal combustion engine, especially in the
case of a cold start. However, the second and any downstream
electric fuel pump may also be switched on when the engine is
operated in the full-throttle range, in order to reach the
increased operating pressure on the pressure side of the second
electric fuel pump from the normal pressure level in the fuel
supply system on the pressure side of the first electric fuel pump.
Using the second and any post-connected electric fuel pump, the
delivered amount of fuel and the attainable fuel pressure may be
controlled in a demand-responsive manner, when the first electric
fuel pump delivers the maximum amount of fuel at a predetermined
pressure while being operated at full power.
[0012] Of course, the fuel supply system of the present invention
may be used for both internal combustion engines having a manifold
injection system and for direct-injection gasoline engines. For use
in direct-injection engines, the fuel supply system has at least
one mechanically driven, high-pressure pump situated hydraulically
nearer to the internal combustion engine than the electric fuel
pumps. For use in internal combustion engines having manifold
injection, all of the fuel pumps of the fuel supply system
exclusively take the form of electric fuel pumps. In this instance,
the presupply pumps would be implemented using several separate
pump stages. The fuel supply system preferably has exactly two
electric fuel pumps.
[0013] The demand-responsive control of the second and any further
electric fuel pump may be implemented in different ways. In
particular, it is conceivable for the fuel supply system to have
control means for adjusting the pressure of the fuel delivered by
the electric fuel pump situated hydraulically nearest to the
internal combustion engine, to a specifiable pressure level. The
specifiable pressure level is preferably variable.
[0014] The control means may take completely different forms. In
particular, it is conceivable for the control means to be a control
unit for switching on and off the electric fuel pump hydraulically
nearest to the internal combustion engine, i.e. the second and/or
any downstream electric fuel pump, or a control unit for varying
the speed of this electric fuel pump.
[0015] It is also conceivable for the control means to have a
controllable control element, which is situated in a return line
from a pressure side of the electric fuel pump situated
hydraulically nearest to the internal combustion engine, to the
fuel tank, or to the suction side of this electric fuel pump. The
control element is preferably electrically controllable, the
control means then having a control unit for controlling the
control element. The control element preferably takes the form of
an electrically controllable pulse valve or an electrically
controllable, proportional, fuel-quantity control valve.
[0016] Furthermore, it is provided that the control element take
the form of a mechanical pressure regulator for adjusting the
pressure prevailing on the pressure side of the electric fuel pump
situated hydraulically nearest to the internal combustion engine,
to the specifiable pressure level. In a further refinement of the
present invention, each of the electric fuel pumps of the fuel
supply system is assigned a mechanical pressure regulator, the
pressure regulators each being situated in a return line from a
pressure side of one of the electric fuel pumps to the fuel tank,
or to the suction side of this electric fuel pump, and the pressure
regulators adjusting the pressures prevailing on the pressure sides
of the electric fuel pumps to different pressure levels. The
different pressure levels preferably increase from the first
electric fuel pump to the electric fuel pump positioned nearest to
the internal combustion engine.
[0017] On the basis of the internal combustion engine of the
species mentioned at the outset, it is provided that, as a further
means for achieving the object of the present invention, the
internal combustion engine have a fuel supply system of the present
invention, including at least two electric fuel pumps connected in
series.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Additional features, options for use, and advantages of the
invention result from the subsequent description of exemplary
embodiments of the invention represented in the drawings. All of
the features described or illustrated here, either alone or in any
desired combination, constitute the subject matter of the present
invention, regardless of how they are combined in the patent claims
or their antecedent references, and regardless of how they are
defined in the description or illustrated in the drawings. The
figures show:
[0019] FIG. 1 a schematic representation of a fuel supply system of
the present invention, for an internal combustion engine having
manifold injection;
[0020] FIG. 2 a schematic representation of a fuel supply system of
the present invention, for an internal combustion engine having
direct injection;
[0021] FIG. 3 a detailed representation of the fuel supply system
of the present invention from FIG. 1, according to a first
preferred embodiment;
[0022] FIG. 4 a detailed representation of the fuel supply system
of the present invention from FIG. 1, according to a second
preferred embodiment;
[0023] FIG. 5 a detailed representation of the fuel supply system
of the present invention from FIG. 1, according to a third
preferred embodiment;
[0024] FIG. 6 a detailed representation of the fuel supply system
of the present invention from FIG. 1, according to a fourth
preferred embodiment; and
[0025] FIG. 7 a preferred embodiment of a control strategy for the
fuel supply system of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] In FIG. 1, an internal combustion engine according to the
invention is designated in its entirety by reference numeral 1.
This includes a fuel supply system 2 for delivering fuel from a
fuel tank 3 into an intake manifold 4 of the internal combustion
engine 1. From there, the fuel travels into combustion chambers 5
of internal combustion engine 1.
[0027] Fuel supply system 2 includes a first electric fuel pump 6,
which pumps fuel out of fuel tank 3 and through a fuel filter 7.
Situated downstream from first electric fuel pump 6 in the
direction of flow is an additional electric fuel pump 8, which
further transports the fuel pumped by first electric fuel pump 6,
into a fuel reservoir 9, from where the fuel travels through at
least one injection valve or at least one injection nozzle 10 into
the intake manifold 4.
[0028] First electric fuel pump 6 produces a pressure of
approximately 2.5 to 6 bar on the pressure side. Second electric
fuel pump 8 increases this pressure to an operating pressure in the
range of approximately 8 to 15 bar. This operating pressure is
applied to the pressure side of second electric fuel pump 8, i.e.
in fuel reservoir 9, for example.
[0029] The two electric fuel pumps 6, 8 connected in series
function as separate pump stages. Instead of only two pumps,
several electric fuel pumps may also be connected in series. The
advantage of connecting several electric fuel pumps in series is
that the second and all subsequent electric fuel pumps 8, but at
least last fuel pump 8 in the direction of flow, may be adjusted to
a separate, variable pressure level (the operating pressure) in a
demand-responsive manner, so as to control pressure and fuel
quantity. The amount of fuel and the fuel pressure are controlled
in a demand-responsive manner, with the aid of second electric fuel
pump 8, when first electric fuel pump 6 delivers the maximum amount
of fuel at full power, given a specified pressure. The increased
pressure level (the operating pressure) may be flexibly adjusted to
any values within a specifiable range. Different options for
controlling the operating pressure are discussed further below.
[0030] During specific operating phases or under specific operating
conditions of internal combustion engine 1, e.g. during a starting
phase of internal combustion engine 1, in particular during a cold
start phase, or during part-throttle operation or full-throttle
operation of internal combustion engine 1, second and any other
electric fuel pump 8 may be selectively switched on. In this
manner, fuel amounts and pressures may be continuously adjusted at
any operating points of internal combustion engine 1.
[0031] FIG. 2 shows a second specific embodiment of an internal
combustion engine 1 according to the present invention. In this
specific embodiment, the fuel transported by fuel supply system 2
is not injected into an intake manifold 4, but directly into
combustion chambers 5 of internal combustion engine 1. Only air
travels into combustion chambers 5 via intake manifold 4. Such
direct-injection gasoline engines operate at a considerably higher
operating pressure than internal combustion engines having manifold
injection (cf. FIG. 1). In the case of direct-injection gasoline
engines, this increased operating pressure is approximately 120 to
150 bar and, in the case of direct injection diesel engines, even
1300 to 1700 bar.
[0032] In order that such a higher operating pressure may be
reached in fuel reservoir 9, a high-pressure pump 11, which is
preferably mechanically driven and transports the fuel delivered by
electric fuel pumps 6, 8, to fuel reservoir 9 at high-pressure, is
provided in addition to the two electric fuel pumps 6, 8. A return
line 11 leads from fuel reservoir 9 back into fuel tank 3, a
pressure-relief valve 12 being situated in return line 11.
High-pressure pump 11 is preferably mechanically driven by a
camshaft of internal combustion engine 1 (not shown). High-pressure
pump 11 is positioned downstream from the two electric fuel pumps
6, 8 in the direction of flow. Connecting two or more electric fuel
pumps 6, 8 in series also has the above-mentioned advantages in the
case of direct-injection gasoline engines 1 having an additional
high-pressure pump 11 positioned in the fuel path.
[0033] Fuel supply system 2 from FIG. 1 for an internal combustion
engine 1 having manifold injection is shown in detail in FIG. 3.
Electric fuel pumps 6, 8 are both situated in fuel tank 3. Stated
more precisely, the two electric fuel pumps 6, 8 are combined to
form a module to be built into fuel tank 3. Electric fuel pumps 6,
8 are situated in a fuel trough 13 in fuel tank 3. This ensures
that sufficient fuel is always available for induction, even when
the surface of the fuel in fuel tank 3 of electric fuel pump 6 is
inclined (e.g. when the vehicle is inclined, or in the case of
transverse or longitudinal vehicle acceleration). Sucking jet
pumps, of which one is exemplarily represented by reference numeral
14 in FIG. 3, ensure that regardless of the position of the fuel
surface in fuel tank 3 in fuel trough 13, a sufficient amount of
fuel is always available as long as fuel is still present in fuel
tank 3.
[0034] Reference numeral 15 denotes a saddle tank, which is
spatially separated from fuel tank 3 by, for example, a drive-shaft
tunnel and only connected to fuel tank 3 by fuel lines 16. Fuel is
exchanged between fuel tank 3 and saddle tank 15 via one or more
additional sucking jet pumps, of which one is exemplarily
represented in FIG. 3 and referred to by reference numeral 17. The
flow of fuel from fuel tank 3 into saddle tank 15 via one of
connecting lines 16 may be varied by an electrically controllable
valve 18. Using a pressure-relief valve 19, the pressure level of
the fuel delivered by first electric fuel pump 6 is kept at an
essentially constant value.
[0035] A pressure sensor 20 is provided at fuel reservoir 9, in
order to measure the operating pressure prevailing in fuel
reservoir 9. A pressure sensor 21 is provided at intake manifold 4
of internal combustion engine 1, in order to measure the
intake-manifold pressure. An optional means of forced induction 22
(for example, an electrically or mechanically powered turbocharger,
supercharger, or the like), an air-mass flow sensor 23, and a
throttle valve 24 are situated in an air-intake tube of internal
combustion engine, upstream from intake manifold 4 in the direction
of flow. A relay for electric fuel pump 6 is denoted by reference
numeral 25. A voltage supply U.sub.Batt and a switching signal Kl15
(terminal 15) from an on-off switch (e.g. of an ignition key or a
switch-on/switch-off button) for internal combustion engine 1 are
applied to relay 25. Electric switching devices or control units
for signal conversion, signal amplification, and control of
electric fuel pumps 6, 8 are denoted by reference numerals 27 and
28.
[0036] Reference numeral 29 refers to a control unit for internal
combustion engine 1, which may take the form of a microcontroller.
Control unit 29 includes a memory element 30, which takes the form
of, e.g. a flash memory. A computer program, which may be run on a
computing element 31 of control unit 29, is stored in memory
element 30. Computing element 31 takes the form of, e.g. a
microprocessor. To execute the computer program, it is transmitted
either in sections, e.g. as instructed, or in its entirety by
memory element 30 to computing element 31 via a data connection 32.
During the execution of the computer program on computing element
31, ascertained results or, other data may be transmitted in the
reverse direction, from computing element 31 via data connection 32
to memory element 30, where they are stored, for example, for
later, further processing.
[0037] The execution of the computer program on computing element
31 allows control signals to be generated for different components
of fuel supply system 2 according to the present invention. In this
context, different control strategies for operating fuel supply
system 2 may be followed. Among other things, a signal 33 for
supplying voltage to pressure sensors 20, 21 is generated in
control unit 29 and transmitted to them. Pressure signal 34
acquired by pressure sensor 20 and pressure signal 35 acquired by
pressure sensor 21 are transmitted to control unit 29. Signals for
controlling relays 25, 26 of electric fuel pumps 6, 8 are denoted
by reference numerals 36 and 37.
[0038] Reference numeral 38 refers to a control signal for first
electrical switching device or control unit 27 of first electric
fuel pump 6. Control signal 38 is, for example, an analog or a
pulse-width-modulated signal. Reference numeral 39 refers to a
control signal for second electrical switching device or control
unit 28 for controlling second electric fuel pump 8. Finally,
reference numeral 40 designates a signal for controlling electrical
control valve 18.
[0039] Signal 39 is a function of different parameters of internal
combustion engine 1, the motor vehicle, and/or the surroundings,
such as of the speed of internal combustion engine 1 and the
surrounding temperature. Electrical switching devices or control
units 27, 28 convert control signals 38, 39 of superordinate
electronic engine control unit 29 to proportional signals for
operating electric fuel pumps 6, 8. In this context, first electric
fuel pump 6 is preferably driven at the maximum feed rate. Second
electric fuel pump 8 is preferably controlled in a variable manner
according to demand. The demand-responsive control of the fuel
amount and the fuel pressure of second electric fuel pump 8 is
adjusted by electronic engine control unit 29 to the operating
state of first electric fuel pump 6 and varied as a function of
this. Control signals 38, 39 of electronic engine control unit 29
may be analog or pulse-width-modulated signals. The control signals
generated by switching devices or control units 27, 28 for
controlling electric fuel pumps 6, 8 are preferably
pulse-width-modulated signals.
[0040] Depending on how second electric fuel pump 8 is controlled,
it delivers more or less fuel to fuel reservoir 9, whereby the
operating pressure prevailing in fuel reservoir 9 increases or (if
fuel is injected into intake manifold 4 of internal combustion
engine and, however, the delivered-fuel quantity of second electric
fuel pump 8 is less,) decreases. In this specific embodiment, the
control means for implementing the demand-responsive adjustment of
the fuel delivered by second electric fuel pump 8 to a specifiable
level of operating pressure therefore include control unit 29
having the control program running on computing element 31, as well
as switching devices or control units 27, 28 for controlling
electric fuel pumps 6, 8.
[0041] A second preferred embodiment of fuel supply system 2 from
FIG. 1 is shown in detail in FIG. 4. Fuel supply system 2
represented in FIG. 4 differs from the one represented in FIG. 3 in
that, in particular, a return line 41 having a control element 42
positioned in it branches off downstream from second electric fuel
pump 8, fuel conveyed by second electric fuel pump 8 being able to
be directed through the return line and back into fuel tank 3.
Control element 42 is electrically controllable and is activated by
a control signal 43 generated by control unit 29. The flow of fuel
through additional return line 41 may be varied with the aid of
control element 42. In this specific embodiment, the control means
for implementing the demand-responsive adjustment of the fuel
delivered by second electric fuel pump 8 to a specifiable level of
operating pressure therefore include control unit 29 having the
control program running on computing element 31, as well as control
element 42.
[0042] Control element 42 may take the form of an electric pulse
valve, which may be a solenoid valve and may be synchronously
triggered in such a manner, that a flow rate through return line 41
is provided that is proportional to the timing, and therefore,
variable, demand-controlled operation of second electric fuel pump
8 is rendered possible.
[0043] Control element 42 may alternatively take the form of a
proportionally opening, electric fuel-quantity control valve, which
is energized or timed with the aid of control signal 43, so that it
proportionally opens as a function of the current flow through it
or the frequency of the timing. In this manner, a cross-section of
the fuel-delivery control valve proportional to the current flow or
the timing is unblocked and a proportional flow rate corresponding
to the unblocked cross-section is provided.
[0044] A third preferred embodiment of fuel supply system 2 from
FIG. 1 is shown in detail in FIG. 5. In this exemplary embodiment,
control element 42 takes the form of a mechanical pressure
regulator 43.
[0045] A fourth preferred embodiment of fuel supply system 2 from
FIG. 1 is shown in detail in FIG. 6. In this exemplary embodiment,
control element 42 takes the form of a mechanical pressure
regulator 43. In addition, first electric fuel pump 6 is likewise
assigned a mechanical pressure regulator 44, which adjusts the
pressure on the pressure side of first electric fuel pump 6 to a
pressure level below the operating pressure. Therefore, each of the
two electric fuel pumps 6, 8 are adjusted to a separate pressure
level by mechanical pressure regulators 43, 44.
[0046] In the exemplary embodiments represented in FIGS. 5 and 6,
the two electric fuel pumps 6, 8, fuel filters 7, and the, or each,
mechanical pressure regulator(s) 43 are preferably combined to form
a module, which is designed to be installed in fuel tank 3. In the
specific embodiments of fuel supply system 2 according to the
present invention, which are represented in FIGS. 3 through 6, it
is also possible for electric fuel pumps 6, 8 to not be controlled
by control unit 29. The operating pressure is then set and
controlled by control element 42 or mechanical pressure regulator
43 alone. In this context, control element 42 may be mechanically
controlled or, for example, electrically controlled by control unit
29.
[0047] A control strategy for fuel supply system 2 of the present
invention is shown in FIG. 7. Different operating states of
internal combustion engine 1 of the motor vehicle are plotted on
the x-axis. The operating pressure in kPa (100 kPa correspond to 1
bar) prevailing in fuel reservoir 9 is plotted on the left side of
the y axis. The demand of internal combustion engine 1 for fuel in
l/h is plotted on the right side of the y axis. In the graph in
FIG. 7, the current fuel demand in the different operating states
is graphically illustrated by a line 50. The two upper lines 51, 52
in the graph represent the operating pressure prevailing in fuel
reservoir 9 at the current operating point, lower line 51 being
valid for a warm internal combustion engine 1 and upper line 52
being valid for a cold internal combustion engine 1. In the case of
a warm and a cold internal combustion engine 1, lines 53 and 54
above and below the operating-pressure curve, respectively,
approximately limit the region in which the actual operating
pressure may move due to pulsations in fuel supply system 2.
Reference numeral 55 indicates the pressure range, which may be
attained by first electric fuel pump 6. The pressure range, which
goes beyond it and is attained by second electric fuel pump 8, is
denoted by reference numeral 56.
[0048] According to the control strategy represented in FIG. 7, an
operating pressure of 2.5 bar (in the case of a warm internal
combustion engine 1) and 3.0 bar (in the case of a cold internal
combustion engine 1) is present in fuel reservoir 9 when the
vehicle stopped. This pressure level may be attained by first
electric fuel pump 6 alone. However, during a starting phase of
internal combustion engine 1, the operating pressure is already
increased to a pressure level of approximately 4.5 bar (for a warm
engine 1) or 10 bar (for a cold engine 1). Second electric fuel
pump 8 is switched on to increase the operating pressure to these
pressure values. During a starting phase of internal combustion
engine 1, internal combustion engine 1 requires an approximately
constant amount of fuel while passing over into idling operation
(LL). Accordingly, the pressure level of 4.5 bar or 10 bar is also
maintained. During the transition from idling operation to
part-throttle operation (TL), the fuel demand of internal
combustion engine 1 increases. Nevertheless, the operating pressure
decreases to a value of approximately 3 bar, curves 21, 22 of the
operating pressure slowly approaching each other as a function of
the surrounding temperature and the operating time of internal
combustion engine 1, since initially cold internal combustion
engine 1 warms up with time.
[0049] During the part-throttle operation of the internal
combustion engine, the operating pressure in fuel reservoir 9 is
kept at an essentially constant level, regardless of the fuel
demand of internal combustion engine 1. This pressure level may be
attained by first electric fuel pump 6 alone, so that second
electric fuel pump 8 may be switched off during this time. However,
as soon as internal combustion engine 1 is operated in
full-throttle region (VL) and the fuel-quantity demand increases,
then the operating pressure steeply rises to values in the range of
approximately 10 bar. To increase the operating pressure to this
pressure level, second electric fuel pump 8 must be switched on
again.
[0050] The increase in the operating pressure during full-throttle
operation allows a higher fuel flow rate to be provided or the
nominal flow rate of an injector 10 at standard pressure to be
reduced. This results in improved mixture preparation [carburetion]
and, consequently, a reduced hydrocarbon (HC) output.
[0051] Fuel supply system 2 of the present invention is suitable,
in particular, for improving the running smoothness and reducing
the fuel consumption and the pollutant emissions. In the case of
manifold-injection engines, it is particularly suitable for
implementing low-emissions designs for future exhaust-gas
legislation.
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